The present invention relates to a process for producing 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone. In more details, it relates to a process for producing 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone from 2,3-dihydro-7-methyl-2-(1-methylethyl)-4H,5H-pyrano[4,3-b]pyran-4,5-dione.
4-Hydroxy-6-methyl-3-(4-methylpentanoyl)-2-pyrone of formula (1): 
is a compound which can be utilized as an active ingredient of insecticides, and it can be obtained by a catalytic reduction of 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl).-2-pyrone of formula (2): 
Therefore, it is useful to afford a process for producing the compound of formula (2).
The present invention has a subject to provide a process for producing 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone that is an intermediate compound for man manufacturing 4-hydroxy-6-methyl-3-(4-methylpentanoyl)-2-pyrone.
The present invention provides a process for producing 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone of formula (2) from 2,3-dihydro-7-methyl-2-(1-methylethyl)-4H,5H-pyrano [4,3-b]pyran-4,5-dione of formula (3): 
under a specific condition. 4-Hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone of formula(2)can be derived to an insecticidal active ingredient, 4-hydroxy-6-methyl-3-(4-methylpentanoyl)-2-pyrone, by a catalytic reduction procedure.
Namely, the present invention provides a process for producing 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone which comprises allowing 2,3-dihydro-7-methyl-2-(1-methylethyl)-4H, 5H-pyrano[4,3-b]pyran-4,5-dione to react with at least one inorganic compound selected from alkali hydroxides, alkaline earth hydroxides, alkali carbonates, alkaline earth carbonates and alkali fluorides in an alcohol, water or a mixture thereof.
The process of the present invention is carried out in an alcohol, water or a mixture thereof.
Examples of the alcohol used for the reaction include lower alcohols, for example, C1-C5 alcohols. Typical examples are methanol, ethanol, 2-propanol and 2-methyl-2-propanol. Amixture of the lower alcohol with water can be utilized as well as a mixture of two or more of the lower alcohols.
In the present invention, the other solvent that is inert to the reaction of the present invention can be used together.
Therefore, the phrase xe2x80x9cin an alcohol, water or a mixture thereofxe2x80x9d means xe2x80x9cin the presence of at least one solvent selected from alcohols and water, and the amount of the solvent is enough for dissolving the inorganic compound selected from alkali hydroxides, alkaline earth hydroxides, alkali carbonates, alkaline earth carbonates and alkali fluorides.xe2x80x9d The amount of the solvent selected from alcohols and water is usually 1 ml to 1000 ml based on 1 g of 2,3-dihydro-7-methyl-2-(1-methylethyl)-4H,5H-pyrano[4,3-b]pyran-4,5-dione.
Examples of the inert solvent include aliphatic hydrocarbons (e.g. hexane), aromatic hydrocarbons (e.g. toluene), ketones (e.g. methylisobutylketone), esters (e.g. ethyl acetate), ethers (e.g. tetrahydrofuran, diethyl ether), amides (e.g. N,N-dimethylformamide), halogenated hydrocarbons (e.g. chloroform), dimethyl sulfoxide, aliphatic nitriles (e.g. acetonitrile), tertiary amines (e.g. triethylamine) and nitrogen-containing aromatic heterocycles (e.g. pyridine).
Examples of the alkali hydroxide include lithium hydroxide, sodium hydroxide and potassium hydroxide, and examples of the alkaline earth hydroxide include magnesium hydroxide, calcium hydroxide and barium hydroxide. In the present invention, alkali carbonate means normal salt of alkali metal carbonate. Therefore, examples of the alkali carbonate include lithium carbonate, sodium carbonate and potassium carbonate. Examples of the alkaline earth carbonate include magnesium carbonate, calcium carbonate and barium carbonate. Examples of the alkali fluoride include cesium fluoride.
An amount of the alkali hydroxides, alkaline earth hydroxides, alkali carbonates alkaline earth carbonates or alkali metal fluorides used for the reaction is usually 1 to 10 moles, preferable 1 to 5 moles against 1 mole of a starting material, 2,3-dihydro-7-methyl-2-(1-methylethyl)-4H,5H-pyrano[4,3-b]pyran-4,5-dione.
The reaction temperature for the process of the invention is usually -20 to 100xc2x0 C., provided that it is usually under a boiling point of a solvent when the boiling point of the solvent used for the reaction is below 100xc2x0 C. The reaction period varies depending on the other reaction conditions and it is usually momentary to 24 hours.
The starting material for the process of the invention, 2,3-dihydro-7-methyl-2-(1-methylethyl)-4H,5H-pyrano[4,3-b]pyran-4,5-dione, can be prepared by a condensation reaction of dehydroacetic acid with isobutyraldehyde in the presence of piperidine in chloroform according to the description of Chemistry and Industry pp. 1306-1307 (1969).
Further, 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone obtained by the process of the invention can be subjected to a reduction, such as hydrogenation in the presence of a transition metal catalyst, to give 4-hydroxy-6-methyl-3-(4-methylpentanoyl)-2-pyrone that is useful as an active ingredient of insecticides.